Morphophonemic Rule
A morphophonemic rule has the form of a phonological rule, but is restricted to a particular morphological environment.
Morphophonemic rules are sensitive to their environment, unlike phonological rules. Whenever morphological information is required to specify the environment for an allophonic rule, the rule is morphophonemic.
- The prefix /in-/ has the allomorphs [il] and [ir]
| /in-/ + responsible | irresponsible |
| /in-/ + logical | illogical |
The rules n G l / __l and n G r / __r are not phonological rules in English, however. If they were, the prefixes /un-/ and /non-/ would also exhibit this regular pattern, but they do not.
| /un-/ + responsive | (*urresponsive) | unresponsive |
| /un-/ + limited | (*ullimited) | unlimited |
| /non-/ + retroactive | (*nor-retroactive) | non-retroactive |
| /non-/ + lethal | (*nol-lethal) | non-lethal |
Therefore, there must be a morphophonemic rule which determines the allomorphs [il] and [ir] of the prefix /in-/.
Payne, Thomas E. (1997) .Describing morphosyntax: A guide for field linguists. Cambridge; New York: Cambridge University Press.
